enclosure question

ok i have an 04 ex cab z71 that im going to out on re se 12 in this weekend. the sub will be a downward firing desgin. my question is that im going to extend the box acrros the back under the seat and use the otherside as the area for my port. is it fesible to have the sub firing down and the port firng to the front of the truck....i can build the box this way and if i dont like it i can cut one side off and have a sealed enclosure..how do you think it would sound?